OF THE MAMMALIAN OSSICULA AUD1TUS. 385 



of importance in the malleus from the same bone in Cebus, except that a rudimentary 

 processus muscularis is to be found halfway down the inner border of the manubrium in 

 Nyctipithecus. The incus, on the other hand, is always high and narrow ; the posterior 

 crus hardly diverges from the body, the slender processus longus diverging considerably. 

 The stapes has long slender crura and a comparatively narrow base. 



In the Squirrel Monkey (Saimaris sciurea, PI. LVIII. fig. 17) the malleus has the 

 general characters described with Cebus ; but the articular surface is still shallower, and 

 the manubrium runs much less nearly in the axis of the body, often forming an angle 

 of not more than 150°. The incus is higher than broad, resembling that of Nyctipi- 

 thecus in its crura, as does the stapes. 



In a single specimen of the malleus and incus of the Black Saki (Pithecia satanas, 

 PL LVIII. fig. 18) the former ossicle has a manubrium rather thicker at the base, and 

 more distinctly flattened laterally (as in most mammals) than in the above-described 

 genera. This process, too, forms the same wide curve seen in Mycetes ; and the incus 

 has the same extremely high narrow body as in the Howlers ; the vertical measurement 

 of the posterior segment is even greater than in those monkeys. 



After careful observation, I consider that the malleus in the Hapalid^e (Marmosets) 

 is intermediate between the same in the Cebidse and in the Nycticeboid lemurs. The 

 description given of the malleus in the genus Cebus will apply to Hapale with two important 

 distinctions — namely, that the articular surface is always narrower and deeper in the 

 Marmoset, and in that animal the whole body is bent more inwards on the manubrium, 

 a character much more prominent in the Nycticebidse, but in Hapale the head of the 

 malleus is longer in its vertical measurement than in Nycticebus. The body of the 

 incus is quite square in H. jacchus ; but in a specimen of H melanura in the College 

 collection it is as high and narrow as in the Douroucoulis {Nyctipithecus felinus and 

 N. trivirgatus). The stapes is of a different form from the type prevalent in the last 

 family. The head is very long ; or, more correctly speaking, the crura are fused half- 

 way to their insertion, where they suddenly diverge towards the base. This is very 

 like the condition seen in many of those marsupials where the crura are not fused 

 throughout. Hence in the genus Hapale may be found the lowest type of ossicle seen 

 in aU the Primates (PL LVIII. fig. 19). 



In Midas (PL LVIII. fig. 20) the malleus is of much the same form as in Hapale, the 

 articular surface also is rather deeper and narrower than in the Cebidae ; but the ten- 

 dency of the body to be bent inwards on the manubrium is not so plainly seen, at least 

 in M. oedipus, rufimanus, and geoffroii, as in Hapale. In all these species the incus is 

 high and narrow. The stapes in M. oedipus has a small head with free crura and a wide 

 aperture ; but one from M. geoffroyii in the College collection has the peculiarities of 

 that ossicle in Hapale. 



The absence of a neck to the malleus of most of the New- world monkeys seems not to 

 be due to an absolute suppression of that part, but rather to its being bent down below 

 the articular surface, and lying actually in the axis of the manubrium. In many mallei 

 from the genus Cebus a slight rounded projection may be detected high up on the outer 

 edge of the handle. In such cases, if the small segment of the manubrium above that 



